Packaging laminates based on cardboard and paper

ABSTRACT

A folded moisture and heat resistant container is manufactured of a material of laminate type in the form of a sheet or a web, said laminate comprising at least a base layer ( 1 ), an outer coating ( 2 ) and an inner coating ( 3 ). The material is at least on one side thereof heat treated in an autoclave. In the material the case layer ( 1 ) consists of a liquid absorbing material, the outer coating ( 2 ) consists of a polymer selected from the group including polypropylene, oriented polypropylene, metalized high density polyethylene, linear low density polyethylene, unmodified polyester, metalized polyester and amorphous polyester, and the inner coating ( 3 ) consists of a polymer selected from the group including polypropylene, high density polyethylene, linear low density polyethylene, unmodified amorphous polyester

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 08/983,588.

FIELD OF THE INVENTION

[0002] The present invention relates to a container which ismanufactured from a material of laminate type in the form of a sheet ora web. More specifically the invention relates to a folded moisture andheat resistant container which is manufactured from a material oflaminate type in the form of a sheet or a web, which material comprisesa base layer, an outer coating and an inner coating, the material on atleast one side thereof being heat treated in an autoclave.

BACKGROUND OF THE INVENTION

[0003] The demand on a container intended for foods is that it should beeasy to manufacture and handle as well as be designed and constructed insuch a way that it gives the best protection possible to the productswhich are to be filled and transported in the container. A good productprotection implies among other things that the container should besufficiently mechanically strong and dimensionally stable in order towithstand the outer influences which the container is exposed to duringnormal handling without the container being deformed or destroyed.Furthermore, the container should be sufficiently physically andchemically impermeable in order to prevent transport of liquid and/orgases through the walls of the container.

[0004] Paper and board are cheap package materials. However, they alsohave drawbacks in rapidly loosing their mechanical strength propertieswhen exposed to liquid or moisture, which results in that a containercontaining these materials becomes flabby and cumbersome. It has thusbeen necessary to improve the properties of the material, either bycoating or lamination.

[0005] Known packaging laminates of this kind comprise a base layer ofpaper or board, which gives the container strength and dimensionalstability, as well as an outer layer of plastic, preferablypolyethylene, which gives the container necessary impermeabilityproperties against liquid and furthermore makes the packaging laminateheat sealable in such a way that two plastic layers facing each othereasily can be sealed by the surfaces being melted together during themanufacturing of the container, whereby mechanically stable liquidimpermeable sealing joints are formed.

[0006] In order to be able to use the packaging laminate in containersfor products of different compositions, the laminate must besupplemented with at least one additional layer of a material withbarrier properties, and the hitherto most used barrier material is ametal foil, preferably an aluminum foil (Al foil). Furthermore, an Alfoil applied on the inside of the laminate must be covered by one orseveral plastic layers, usually polyethylene, in order to preventcontact between the Al-foil and the later on filled food.

[0007] It has thus always been a wish within the packaging technology tofind alternative package materials in which liquid absorbing fiberlayers are not used, these materials in practice thus being completelyfree from the disadvantages of the known package materials based onpaper or cardboard.

[0008] Such a known alternative package material has for example astrengthening base layer of plastic and a filler intermixed with theplastic, and this material has proved to be less moisture sensitive thanthe previously used materials based on paper and cardboard.

[0009] Furthermore, it is often required that a container intended forfood is constructed in such a way that it allows aseptic filling of aproduct which is sterilized and filled under sterile conditions in alikewise sterilized container which after filling is sealed in such away that while stored before being consumed the filled product is notre-infected by harmful micro-organisms.

[0010] Concerning the filled product, it has for a long time been knownthat the shelf life of a foodstuff can be prolonged by the foodstuffbeing subjected to a heat treatment which is so extensive thatmicro-organisms present in the foodstuff are completely killed orreduced in number. In order to achieve an adequate heat treatment thetreatment must be performed in such a way that all parts of the treatedproduct once and for all is heated to such an extent and for such a longtime as is required for obtaining the desired killing or inactivation ofmicroorganisms in the product.

[0011] A heat treatment for killing and/or inactivation ofmicro-organisms can be accomplished by means of moist as well as dryheat. In the food industry a heat treatment in moist heat is preferredsince the biological killing and inactivating mechanisms are much moreeffective at a high water content than at a low water content, i.e. dryheat. Besides, the heat transfer in the equipment used for heattreatment is much more effective with moist heat.

[0012] However, known containers of a packaging laminate with a liquidabsorbing fiber layer cannot be used for heat treatment with moist heatwithout the desired mechanical rigidity of the packaging laminate andthus the dimensional stability of the container being impaired or lost.

SUMMARY OF THE INVENTION

[0013] The purpose of the invention is thus to provide a moisture and/orheat resistant packaging container made of a laminate material of theabove mentioned type.

[0014] In order to achieve this purpose the packaging material accordingto the invention is formed from a laminate in the form of a sheet or aweb which on at least one side thereof is heat treated in an autoclave.This laminate comprises at least one base layer consisting of a liquidabsorbing material, an outer coating, and an inner coating. The outercoating consists of a polymer selected from the group consisting ofpolypropylene, oriented polypropylene, metalized oriented polypropylene,high density polyethylene, metalized high density polyethylene, linearlow density polyethylene, unmodified polyester, metalized polyester andamorphous polyester. The inner coating consists of a polymer selectedfrom the group consisting of polypropylene, high density polyethylene,linear low density polyethylene, unmodified polyester and amorphouspolyester.

[0015] In order to explain the invention in more detail reference ismade to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 schematically shows a cross section through a packaginglaminate in the form of a sheet or a web according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Like conventional packaging laminates, the packaging laminate inFIG. 1 comprises a relatively thick strengthening base layer 1 as wellas an outer coating 2 and an inner coating 3. An outer and an innercoating refers to a coating which is applied on the outside or theinside of the laminate, respectively.

[0018] The packaging laminate has as an essential part a base layer 1 ofa liquid absorbing material. Other layers in the packaging laminate canalso include liquid absorbing materials. However, these are not soimportant for the container stability as the base layer with itsmechanical strength properties.

[0019] The liquid absorbing material in the base layer 1 preferablyconsists of paper or cardboard. Other water absorbing materials used inpackaging laminates are for example ethylene/vinyl alcohol, i.e. anethyl-vinyl alcohol copolymer (EVOH) and polyvinyl alcohol. Thesepolymers rapidly loose their barrier properties if they are exposed tomoisture.

[0020] It has surprisingly been shown that containers made of a laminateof the above mentioned type not only withstand the usual heat treatmentbut also a treatment under extreme conditions in a humid environment ifthe laminate with the above mentioned liquid absorbing base layer 1 alsocomprises the outer coating 2 as well as the inner coating 3 with thealternative components indicated below in the laminate layers.Furthermore, the cut edges on the packaging laminate in the completedcontainer should be protected.

[0021] In order to withstand a strong influence of moisture in the formof water as liquid or steam the coatings 2 and 3 are according to theinvention designed to be heat resistant and to have good vapor barriers.Thus, the outer coating 2 consists of a polymer which can bepolypropylene, oriented polypropylene, metalized (usually with aluminum)oriented polypropylene, high density polyethylene, linear low densitypolyethylene, metalized high density polyethylene, unmodified or “clean”polyester, metalized (usually with aluminum) oriented polyester oramorphous polyester. The inner coating 3 consists of a polymer which canbe polypropylene, high density polyethylene, linear low densitypolyethylene, unmodified polyester or amorphous polyester.

[0022] The material for the coating layers must be able to withstand thehigh temperatures of autoclaving which is approximately 105-122° C.Therefore, materials such as low density polyethylene are generally notused as a coating material due to its relatively low melting temperaturewhich is approximately 102-112° C. The present invention uses highermelting polyethylenes capable of withstanding autoclavation. Thesepolyethylenes include linear low density polyethylene which has amelting temperature of approximately 115-123° C. and high densitypolyethylene which has a melting temperature of approximately 123-135°C.

[0023] The polyester material, for example, may be polyethyleneterephthalate, PET, i.e. a polyester which comprises terephthalic acidand ethylene glycol. In order to work in the coating process and notgive rise to an off-flavor, a small amount, about 1.5-2.5 weight percentof glycol/cyclohexanedimethanol is added to this polyester. The mainobjective of this additive is to reduce the crystallinity rate of thematerial.

[0024] Preferably, the packaging laminate according to the inventionalso has a barrier layer 4 arranged between the base layer 1 and theinner coating 3, which barrier layer 4 is intended to be facing thefilling material of the packaging container. The barrier layer canconsist of aluminum, a silica coating, ethylene/vinyl alcohol, polyvinylalcohol, metalized (usually with aluminum) oriented polypropylene, analuminum oxide coating or metalized (usually with aluminum) orientedpolyester, the polyester for example being polyethylene terephthalate.

[0025] Furthermore, the packaging laminate according to the inventioncan have a layer 5 arranged between the base layer and the outer coating2, which layer 5 can consist of polypropylene, low density polyethylene,medium density polyethylene, high density polyethylene or amorphouspolyester, the polyester for example being polyethylene terephthalate.An additional similar layer can be arranged on the other side of thebase layer 1.

[0026] Finally, the packaging laminate according to the invention canhave a coating 6 adjacent one or both sides of the barrier layer 4,which coating 6 can consist of an adhesive plastic, a heat sealableplastic (e.g. polyethylene), a primer or a lacquer. An additional layercan be incorporated between the base layer 1 and the adjacent coating 6,which layer then preferably consists of one of the above mentionedcomponents for the layer 5.

[0027] Consumer containers ready for use and of throw-away type areaccording to known technology manufactured by folding from a web of apackaging laminate according to the invention to a tube in such a waythat the two longitudinal edges of the web are joined in a longitudinaloverlap seam. The tube is filled at 80-90° C. with the filling materialin question and is divided into closed container units by repeatedlateral sealing of the tube beneath the level of filling material in thetube. Container units filled by means of this web filling method areseparated from each other by cuts in the transversal sealing zones andthe desired geometrical final form is obtained by an additional formingand sealing operation.

[0028] The packaging laminate according to the invention is not onlyadapted to the above mentioned treatment but also to more drasticconditions including moisture and/or heat. Thus, containers manufacturedfrom these laminates are very suitable f or preservation byrefrigeration as well as preservation by heat. When preservation byrefrigeration is used these containers having solid and/or liquidfilling material can be chilled by means of water cooling.

[0029] Furthermore, the laminate according to the invention has beenshown to be very suitable for manufacturing dimensional stableimpermeable packaging containers which can be used at highly extremeconditions in a humid environment including heat treatment with moistheat and a pressure above the atmospheric, at least one of the sides ofthe container being exposed to a humid atmosphere and heat treatment.Such harsh environments comprise autoclaving at temperatures and periodswhich are customary for foods. This means that the laminate is alsoextremely suitable to be used for producing a container which isintended for being filled with a product under aseptic conditions. Inthis connection the product is sterilized and filled under almoststerile conditions in a likewise sterilized container which afterfilling is sealed in such a way that during storage the filled productis not re-infected by micro-organism before it is consumed.

[0030] When such a packaging procedure, a so called hot fill, is usedthe filling material is thus filled according to known technology whilestill being hot in sterilized, preferably heat sterilized containers.Such a treatment results in that the container is exposed to moist heatat a temperature of the filling material of 75° C., preferably 90° C.,or more.

[0031] During a subsequent cooling phase containers exposed to the abovementioned example of heat treatment Will also be subjected toenvironments in which good sealing properties of the container againstmoisture and liquid are required. During the cooling phase the fillingmaterial is allowed to cool in the container which is manufactured froma laminate. This cooling can for example take place in a fluid bath andalso by spraying with cold water, if necessary with accompanying coolingwith CO₂ or N₂ in order to rapidly be able to achieve a sufficiently lowtemperature, such as 4° C.

[0032] The above mentioned harsh environments comprise autoclaving attemperatures and periods customary for food. In this connectionautoclaving means sterilizing or killing micro-organisms in a vessel, inwhich the heating takes place under pressure, usually with steam or airas a heat transfer medium.

[0033] At a temperature in the autoclaving vessel within the interval105-121° C. an established reference temperature is chosen to be 121.1°C. (250° F.) and a z-value (a temperature alteration for changing thereduction time for a certain micro-organism with a factor 10) to be 10°C. The heat treatment value Fr which is determined in this area is oftenrepresented by F₀. (F₀=Fr at 121° C.). The heat treatment value Fr isthus the combined lethal effects at the temperatures used in practice.When the temperature lies within the interval 90-105° C. duringproduction a reference temperature of 93.3° C. (200° F.) and a z valueof 10° C. are used. For pasteurization a reference temperature of 65.5°C. (150° F.) and a z value of 5° C. are used. Other standardizedreference temperatures are used at special occasions.

[0034] Products included in a container according to the invention arenot heat treated to a special Fr value, on the contrary to a certaincenter temperature guaranteeing a product which is sufficiently heattreated. (The position of the center point depends of course on theconstruction of the container as well as the product in the container.)

[0035] Containers according to the invention have been shown to beuseful for liquid products requiring an F₀ value of 3-5, forviscous/semi-solid products requiring an F₀ value of 6-10 and also forhard products requiring an F₀ value of 12-18, the F₀ values of coursebeing dependent of the volume of the container.

[0036] While a number of embodiments of the invention have beendescribed in detail above, it should be obvious to persons skilled inthe art that various modifications and adaptations can be made withoutdeparting from the spirit of the invention and the scope of the appendedclaims.

What is claimed is:
 1. A folded moisture and heat resistant containermanufactured from a laminate in the form of a sheet or a web, saidlaminate comprising at least one base layer, an outer coating and aninner coating, said laminate on at least one side thereof being heattreated in an autoclave, characterized in that the base layer consistsof a liquid absorbing material, the outer coating consists of a polymerselected from the group consisting of polypropylene, orientedpolypropylene, metalized oriented polypropylene, high densitypolyethylene, metalized high density polyethylene, linear low densitypolyethylene, unmodified polyester, metalized polyester and amorphouspolyester, and the inner coating consists of a polymer selected from thegroup consisting of polypropylene, high density polyethylene, linear lowdensity polyethylene, unmodified polyester and amorphous polyester.
 2. Acontainer as claimed in claim 1, wherein said base layer consists ofpaper or cardboard.
 3. A container as claimed in claim 1, wherein saidlaminate additionally includes a barrier layer between the base layerand the inner coating, said barrier layer comprising a material selectedfrom the group consisting of aluminum, an aluminum oxide coating, asilica coating, ethylene/vinyl alcohol, polyvinyl alcohol, metalizedoriented polyester and metalized oriented polypropylene.
 4. A containeras claimed in claim 1, wherein said laminate additionally includes alayer between the base layer and the outer coating, said layer beingselected from the group consisting of polypropylene, low densitypolyethylene, medium density polyethylene, high density polyethylene andamorphous polyester.
 5. A container as claimed in claim 3, wherein saidlaminate additionally includes a coating adjacent one or both sides ofthe barrier layer, said coating being selected from the group consistingof an adhesion plastic, a heated sealable plastic, a primer and alacquer.
 6. A container as claimed in claim 1 wherein said laminate iscapable of withstanding heat treatment in an autoclave at a temperatureof approximately 105-122° C. and at a pressure at above or greater thanatmosphere.